This invention relates in general to the field of printing and, more particularly, to a system admixture compensation system and method.
Full-color printing on offset presses has become relatively reliable and affordable for clients long accustomed to printing in black and white or with just one or two pre-mixed spot inks. Such printing utilizes photo-chemical processes to reduce original multi-colored materials to the four constituent colors used in printing. For example, printed color images currently typically combine different intensities of four basic colorsxe2x80x94Magenta (xe2x80x9cMxe2x80x9d), Yellow (xe2x80x9cYxe2x80x9d), Cyan (xe2x80x9cCxe2x80x9d), and Black (xe2x80x9cKxe2x80x9d)xe2x80x94using a printing process known as four-color-process printing. In practice, accurately printing a color image to a customer""s satisfaction is often times tedious, problematic and time consuming, as it usually requires manual intervention. For example, conventional four-color-process printing usually utilizes presses that are only designed to either apply or not apply a single amount of ink to any given location on a page. To reduce the number of errors and expenses associated with errors in acceptable print quality off the press, proofs are usually used.
To illustrate, four-color-process printing requires a reliable color proof for use as a guide for press operators and customers in finalizing a printing press to perform a production print job. For example, the proof conveniently and inexpensively provides a printing prototype for a customer to approve color appearances to be used on a production print job, in an easily-changed and viewable image. A single piece of film for each of the four colors is also required by the platemaker to make thin printing plates that are wrapped on the drums of the printing press, covered with the appropriate inks, which are then indirectly rolled over sheets of paper during the printing process. Computer-to-Plate (CTP) technology can eliminate the need for film in the plate-creation process.
Traditional attempts in performing or addressing aspects of the color management process for Reflective Multi-Color Reproduction Systems (RM/CRSs) include approaches which typically suffer from compromises and results that in many cases customers in the printing industry feel are unsatisfactory. For example, traditional quality control specifications such as Specifications Web Offset Publications (SWOP) have utilized solid ink density, ink color (hue)/sequence, and dot gain and print contrast to control variables, with only limited success.
Unfortunately, a proof includes inherent tone and color differences from a press sheet, and a great deal of time is consumed in assessing how to improve the coincidence of the tone and color reproduction characteristics of a press to those of a proofing system. Moreover, SWOP specifications do not typically discuss several variables such as proportionality failure rates, system admixture characteristics, and color gamut mismatches that color scientists use in characterizing color reproduction. International Color Consortium (ICC) color management systems have also attempted to address the color management process by utilizing colorimetry measurements, usually in a single graphic data file multi-dimensional transformation process, but practitioners in the printing press industry usually believe that this type of adaptation is inadequate. These systems also fail to separate or compensate for these variables. ICC-colorimetry based color management systems also attempt to map points on a larger color gamut to a nearest point on a smaller color gamut by a variety of corrections, such as relative or absolute colorimetric or photometric. Unfortunately, this type of gamut mapping has typically resulted in compromises that are unacceptable in the printing industry. Moreover, these systems usually attempt to map colors to be used with a proofing device, which usually has a larger color gamut, to those to be used with a printing device, which usually has a smaller color gamut. These systems and methods typically limit the output achievable by a printing press.
Unfortunately and for example, the SWOP approach suffers from inconsistencies and inaccuracies because, among other things, this approach utilizes dot gain and print contrast measurements, which may not provide the right measurements to perform aspects of accurate color management. Moreover, these systems and methods do not consider varying effects from the principle variables that ultimately should be addressed in the color management process. For example, tonal reproduction characteristics vary widely with characteristics of a reflective reproduction device such as electrophotographic, thermal, laser and inkjet printers, and offset lithography, letter press, gravure, and flexography printing presses and peripheral conditions, and traditionally are reported as dot gain and print contrast. Many of these variations that may be caused by fluctuations in press printing conditions"" printing characteristics including, but not limited to, variations due to paper/base substrates, inks, plates, fountain solutions, image transferring cylinder blankets, press mechanical settings and ambient moisture/temperature conditions may change batch-to-batch or day-to-day. These fluctuations usually affect the printing device""s reproduction characteristics during each production print job and, unfortunately, it is not practical to track down causes of these fluctuations.
From the foregoing, it may be appreciated that a need has arisen for a system admixture compensation system and method. In accordance with teachings of the present invention, a system and method are provided that may substantially reduce or eliminate disadvantages and problems of conventional printing systems.
Aspects of the invention may provide several important advantages. Various embodiments of the invention may have none, some, or all of these advantages. For example, one aspect of the invention is a method for gathering data such as density data that provides more control in the color management process. The method includes providing reference profile density values for at least one color combination having a plurality of colors produced by a reference device using a reference colorant set. The reference colorant set has reference initial percent dot values (IPDVs) for the at least one color combination. The method also includes providing current profile density values for at least one color combination produced by a current device using a current colorant set. The current colorant set has current IPDVs for the at least one color combination. The method also includes quantifying reference theoretical percent dot values (TPDVs) as efficiency attributes using the reference colorant set and quantifying current TPDVs as efficiency attributes using the current colorant set. The method also includes calculating percent dot value correction factors that compensate for at least one difference between image data produced with the reference colorant set and image data to be printed with the current colorant set in response to the reference efficiency attributes and the current efficiency attributes, the factors to be used to adjust and generate the image data to be printed. Such calculations may provide substantially representative characteristics of a full tonal scale (1-100%) for press and/or proofing conditions, and the ability to provide factors that may be applied to, for example, digital representations of images, at a computer-to-plate (CTP) or direct imaging press production phase. In other words the accuracy, with which the appearance of the outputs of one reflective reproductive system may be made to correspond to another, may be improved.
Another aspect of the invention may also provide for separately compensating for two of five principle variables. For example, one embodiment of a system admixture compensation method includes identifying system admixture characteristics of data produced by a reference colorant set as reference TPDVs in response to reference profile density values and reference IPDVs. The method also includes identifying system admixture of data produced by a current colorant set as current TPDVs in response to current profile density values and current IPDVs. The method also includes providing color gamut density adjustment factors (CGDAFs) if the sum of at least one of the factors and a corresponding at least one of the initial reference IPDVs exceeds 100 percent. The CGDAFs may correct the color gamut mismatch and at least one of the factors may be calculated by determining a control component and calculating a product of a first value equal to a targeted solid major density aimpoint of the control component and the at least one factor, and a second value equal to a reference TPDV, for the control component, that is required to achieve a measured density for at least one of a plurality of color channels if a system using the reference colorant set had perfect efficiency divided by a current TPDV, for the control component, that is required to achieve a measured density for at least one of a second plurality of color channels if a second system using the current colorant set had perfect efficiency to obtain the at least one factors. In addition, at least one of the factors compensates for at least one difference between image data produced with the reference colorant set and image data to be printed with the current colorant set and is used to adjust and generate the image data to be printed. Such advantages provide the present invention the advantage of compensating for differences between multiple colorant sets and their corresponding RM/CRSs with different additivity failure characteristics, for a variety of systems.
Another aspect of the invention may also separate out factors that may be caused by fluctuations in printing press and peripheral printing conditions"" printing characteristics that affect the printing device""s reproduction characteristics. These fluctuations include, but are not limited to, variations due to paper/base substrates, inks, plates, fountain solutions, image transferring cylinder blankets, press mechanical settings, ambient air conditions, ambient moisture conditions, ambient temperature conditions, and chemical residue conditions, which may change batch-to-batch or day-to-day. Chemical residue conditions vary with characteristics of, for example, plate or blanket wash chemistry, roller residue, wear and tear on press components, and a variety of ambient air conditions.
Another aspect of the present invention is a data form. The system admixture data form includes a first column representing a plurality of one-dimensional color control regions produced using a colorant set. The first column is located approximately along a first axis generally parallel to an output path of a press output device. The system admixture data form also includes a second column representing a plurality of multi-dimensional color control regions produced using the colorant set. The second column is located approximately along a second axis generally parallel to and at a lateral spacing from the first column. The first axis and the second axis are positioned proximate to one another and the lateral spacing does not exceed a predetermined distance. In a particular embodiment, the predetermined distance does not exceed 25 millimeters. In yet another embodiment, the second column is selected from the group consisting of the magenta, red, green, cyan, yellow, blue, and neutral families.
One embodiment of a system admixture data form provides for arrangement of data in color families. The present invention provides the advantage of allowing for the use of color image editing engine (CIEE) functionality, which allows adjustments to be made to all color families as desired. The present invention provides the advantage of providing suitable color samples for which applicable measurements may be taken. In addition, one or more aspects of the present invention may provide the advantage of reducing calculation inaccuracies by reducing any differences in ink film thickness and tone reproduction characteristics between measurements. Such an advantage may reduce system errors that affect color manageability.
Another aspect of the invention may also provide for calculation of CGDAFs, which may reduce or remove the effects of compromises reached by traditional color management systems"" photometric or colorimetric corrections. Moreover, CGDAFs may be utilized in a method in conjunction with percent dot value color correction factors (PDCCFs) and/or secondary PDCCFs to calculate a density that corresponds to a larger than 100% dot value to be used with a printing device, which usually has a smaller color gamut, to those to be used with a proofing device, which usually has a larger color gamut. Other technical advantages may be readily ascertainable by those skilled in the art from the following figures, description and claims.